A contemporary comparison of crossbred ewes from five crossing sire breeds was made on a research farm from 1976 to 1981. The breeds involved were the traditional Border Leicester, three imported breeds — the East Friesian, the Oldenburg and the Texel, and a new prolific composite breed — the Cambridge. Rams from these breeds were group mated (2 to 3 rams per breed per year) to Scottish Blackface ewes on an upland farm in Scotland. Crossbred ewes derived from these matings were compared over three lamb crops on a lowland farm in England. The ewes were run together with the same husbandry conditions for all types. Results were available on some 120 to 150 ewes (300 to 450 lambings) per crossbred type. The Oldenburg and Texel crossbred ewes were appreciably poorer in most aspects of lowland lamb production. The Cambridge crosses were prolific but had high lamb mortality and lower litter weights at weaning than the traditional Border Leicester crosses. The East Friesian crosses were appreciably superior in several production traits. These results were combined with those from three other trials, involving crosses from the Bluefaced Leicester and Animal Breeding Research Organisation Damline to provide a ranking for UK crossing sire breeds.